Apparatus for evaporating a material within an ion pump



Feb. 11, 1964 c. E. BERRY 3,121,155

APPARATUS FOR EVAPORATING A MATERIAL WITHIN AN ION PUMP Filed Sept. 4,. 1962 97 if 65 66 INVENTOR.

(m -mp0 5. 5520/ United States Patent 3,121,155 APPARATUS FOR EVAPORATING A MATERIAL WlTHIN AN ION PUMP Clifford E. Berry, Altadena, Calif., assignor to Consolidated Vacuum Corporation, Rochester, N.Y., a corporation of New York Filed Sept. 4, 1962,. Ser. No. 220,975 4 Claims. (Cl. 219-19) This invention relates to ion pumps and, more specifically, to a source of gettering and replacement material for cold-cathode and hot-cathode ion pumps.

The use of ion pumps as vacuum pumps has become Widespread within the past few years. Generally, such ion pumps may be divided into two classes, cold-cathode ion pumps and hot-cathode ion pumps. Cold-cathode ty'pe ionpumps utilize the phenomenon known as the Penning discharge. Examples of such an ion pump are shown in US. Patent No. 2,993,638, issued July 25, 1961, L. D. Hall et al., inventors. An example of a hot-cathode type of ion pump is given in US. Patent No. 2,850,225, issued September 2, 1958, R. G. Herb, inventor.

The conventional hot-cathode type of ion pump relies upon the continuous evaporation during operation of a gettering or replacement material to coat the pumping surfaces of the device. However, in the cold-cathode type of ion pump described in the aforementioned patent, no such source of gettering or replacement material is provided. Coapending US. Patent applications, Serial No. 815,351, filed May 25, 1959, and Serial No. 815,352, filled May 25, 1959, each assigned to the assignee of the present application relate to improved ion pumps of the cold-cathode type in which the operation of the pump includes the deposition on the pumping surfaces of replacement or gettering material.

According to the present invention, a novel method for providing evaporation of gcttering or replacement material is provided by winding or twisting a wire of the material to be evaporated about a carrier-wire. The entwined wires are wound upon a feed reel and the carrier-wire is stretched between the feed reel and takeup reel. The two wires are gradually unwound from the feed reel and, while passing between the feed reel and takeup reel, the wire of the material to be evaporated is vaporized. While conventional means may be utilized to accomplish the evaporation, in a particular embodiment, a special auxiliary structure is utilized to accomplish evaporation by resistiveheating.

The invention may be more readily understood by referring to the accompanying drawings in which:

FIGURE 1 is an elevation of an embodiment of the invention utilizing radiation heating to accomplish evaporation;

FIGURE 2 is an elevation of an embodiment of the invention utilizing resistive heating to accomplish evaporation; and

FIGURE 3 is a plan view of the embodiment of FIG- URE 2.

Referring now to FIGURE 1, there is shown a device for use in evaporating gettering or replacement material in a vacuum pump, which may be either of the hotcathode or cold-cathode type. The pump has a wall 11 of insulating material, preferably, within which are disposed a first pulley 12 and a second pulley 13. The pulleys 12 and 13 are attached to axles 14 and 15 respectively, which are journalled to the wall ll by bearings 16 and 17, so that the pulleys 12 and 13 and axles 14 and 15 may rotate. A heater element 19 is connected between a pair of conductors 20 and 21 which pass through the wall 11 and are insulated therefrom by insulators 22, 23. Outside the wall 11 the conductors 20, 21 have a battery 24 connected therebetween.

A feed reel 25 and a takeup reel 26 are shown within the wall 11 as partially broken away. The feed reel 25 has wound thereon a plurality of wires 27 which are twisted together to form the feed of material to be evaporated. As used herein, the term twisted comprehends any conventional method of fixing the two types of wires together, actual twisting being the simplest. The plurality of wires 27 consists of one or more refractory carrier-wires 28 and one or more wires of the material to be evapoated. The two types of wires are twisted together to form a single entity and then are wound about the reel 25. The refractory carrier-wire 28 passes about the pulley 13 and on to the takeup reel 26. However, the heat from the heater element 19 causes the wire of material to be evaporated, to evaporate as it passes adjacent the heater element 19, and so this Wire is not wound on the talceup reel 26.

Rotary drive for the operation of the feed system may be operated by any conventional drive system. For example, a magnetic clutch arrangement may be utilized to rotate the takeup reel 26 and a brake system utilized in conjunction with rotation of the feed reel 25 to insure that the wire extended between the two reels is under tension. The refractory carrier-wire may be of any conventional material such as tungsten, molybdenum or rhenium, which will not readily melt or evaporate at the temperature of operation of the device. The material to be evaporated, as used herein, refers to any of the conventional getter or replacement materials described in the aforesaid Patent No. 2,850,225 or application Serial No. 8l5,352. It will, however, be understood that the use of titanium is preferable, due to its wellknown characteristics with respect to ion pumps.

As an example, two tungsten wires of ten mil diameter may be twisted together with two titanium wires of ten mil diameter and wound upon the feed reel 25. The rate of feed will depend upon the characteristics of the pump and the rate at which the element 19 provides for evaporation of the material. 19 has been referred to as a heater element, it will be appreciated that it may equally well be an element to provide evaporation by electron bombardment of the wires.

While the device of FIGURE *1 provides for satisfactory operation in evaporation of material, the device is comparatively inefiicient, when either of the aforementioned methods of evaporation are used. In FIGURE 2 there is shown a plan view of a system by which resistive heating is utilized toprovide for more efiicient evaporation of the material. In FIGURE 2 there is shown a device 36 for evaporating material within an ion pump wall 31. The material consists of twisted together wires 27 wound on feed reel 25 and having a carrier wire 28 extending to, and wound about, takeup reel 26. The feed reel 25 attached to an axle 35 which is journalled to the wall 31 by a first portion 36 of a magnetic clutch. A second portion 37 of the magnetic clutch is connected by a drive shaft 33 to a motor 39. Rotation of the motor 39 causes the takeup reel 26 to rotate, so as to draw the carrierwire 28' from the feed reel 25 over a pair of pulleys 40 and 41. The pulley 40 is attached to an axle 43 which is journalled to the wall 31 by a bearing 44. The pulley 41 attached to an axle 45 which is journalled to the wall 31 by a bearing 46. The axles 43 and 45 are made of an electrical insulation materialit the wall 31 is an electrical conductor so as to provide electrical insulation between the two axles 43 and 45. Alternatively, any other method of providing electrical insulation between the pulleys 40, 41 may be utilized.

Depending downwardly from the pulley 40 are a pair of conductors 48 and 49. The conductors 48 and 49 extend into a container 50 which is filled with a liquid 51.

Further, while the element 3 "I he container 50 rests on a shelf 52 which is supported by a shield 53 attached to the Wall 31 and the shelf 52. The shield 53 has an aperture 54 through which the twisted wires 27 extend after passing over the pulley 40. The pulley 41 has a similar pair of conductors 55, 56 depending downwardly therefrom into a container 57 filled with a liquid 58 and similarly supported on the shelf 52 by a shield 59. The shields 53, 59 prevent the deposition of the evaporated material on the tanks 56', 7 and pulleys 4A1, 41. Similar shields can be used with the device of FIGUREl, if desired. An. electrical terminal 60 is in contact With the fluid Sll and is electrically connected to a conductor 61 which extends through an insulator 62 in the wall .31 to one terminal of a battery 63. A lead 64 is connected to the other terminal of the battery 63 and extends through an insulator 65 in the wall 31 and is connected to an electrical terminal 66in contact with the fluid 58. The conductor 61 extends through an insulator 67 in the shelf 52 and container Sit and the conductor 64 extends through an insulator 63 in the shelf 52 and container 57.

FIGURE 3 is a plan view of the device of FIGURE 2., taken along lines'3 3 thereof. FIGURE 3 more clearly indicates the wrap angle of wire 27 about the reel 40 and the wire 28 about the reel 41 which is necessary to provide the necessary electrical contact between the wires and pulleys for'the tension at which the wires are being unreeled.

In operation, the device of FIGURES 2 and 3 provide evaporation of the material by resistive heating. In order to accomplish this, the fluids 51 and 5-8 in containers 50 land 57 are electrical conductors. If, as willordinarily be the case, the pump is to be operated at room temperature, the material selected is a fluid at such temperature. Thus,

7 preferably, one of the elements which is an electrical conductor and a liquid at room temperature should be selected. This requirement will normally limit the fluid selectedto one of the materials which is a liquid at room temperature, i.e., mercury, cesium, rubidium and gallium. However, since the device is a vacuum pump, care must be taken in selecting the fluid: tolprovide a fluid which has an essentially low vapor pressure at the temperature of operation. Of the four elements mentioned, gallium is therefore preferred for normal operating conditions as a result of its boiling point 0131983 0. and its melting point of 29.78 C. Thus, only a slight elevation in room temperature fromthat normally encountered is necessary to bring the gallium into the liquid state.

The device of FIGURES Ziand 3 is particularly advantageous where high vacuums are to be utilized since at such vacuums, resistive heating through electrical contact by conventional means is not satisfactory. Thus,

it has been found thatythe use of conventional commuta -tors or similar conventional practices is not satisfactory at high vacuums due to a binding between the various 7 moving components of the electrical circuit, as for example, the metal commutator ring and carbon commutator brush. However, the use of the present invention and particularly gallium results in ga goodelectrical connection by eliminating binding while at the same time notadding significantly to the molecules of material within-the ion pump which'mustrbe evacuated to main tain the desired pressure.

In typical operations, cur-rentof ten to fifteenamperes provides satisfactory evaporation in the device of FIG URES 2 and 3. It will,thus, be understood that the battery 63, as is of. course true for the -battery24, is

shown byway of illustration only as a source of-electrical current. Either alternating or direct currentfromany conventional sourcemay of cour's e be utilized with the ydevice'of FIGURES 2 and 3. I V r V Y terial to 'be evaporated is formed While the device of FIGURES 2 and 3, as shown, includes the use of the pulleys 40, 41,'it will be understood that the invention may also be practiced by making electrical contact directly with the feed and take reels. However, in such an embodiment, control over evaporation is necessarily much less precise since current, in some degrees, flows through the entire length of material to be evaporated. Therefore, such an embodiment is not preferred. In order to avoid this disadvantage, it is possible to use only one pulley, i.e., the pulley adjacent the feed reel. Also, it will be understood that, in the device of FIGURE 1, the pulleys function primarily to fix the location of the wires, since unwinding causes the point at-which the twisted wires leave the \feed reel to gradually move toward the center of the feed reel. However, the use of the reels is not essential to the operation of the device in its most elementary form.

The invention claimed is:

1. Apparatus for evaporating a material within an ion pump comprising a carrier wire composed of refractory material,

a material to be evaporated, said material to be evaporated being carried by said carrier wire,

a feed reel about which said carrierwire and said material to be evaporated pass,

a takeup reel about which said carrier wire passes,

means for unwinding the carrier wire and material to be evaporated from the feed reel and for winding the carrier wire onto the takeup reel, and

means for initiating a flow of electrical current through the carrier wire during its passage between the feed reel and takeup reel, including (a) a first fluid container,

(b) a second fluid container,

(c) an electrically conductive fluid in each of said containers,

(d) a source of electrical current connected between the fluids in said containers,

(e) a first electrical conductor extending into the first container so'as to-be in electrical contact with the fluid therewithin,

(f) firstmeans forming an electrical circuit between the first electrical conductor and the car- (g) a second; electrical conductor extending into the second fluid container so as to be m electrical contact with the fluidtherewithin, and

(h) second means forming an electrical circuit between the second electrical container and the carrier wire.

means forming an electrical circuit includes a first pulley disposed adjacent the take up. reel and the second means forming an electrical circuit includes a second pulley adjacent the feed reel, and inwhich the carrier wire passes around the first and second reels. f

3. The apparatus ofclaim '2 and inwhich the fluid in the containers is gallium. i

4.- The apparatus of-claim 3 and in which the matwisted with the carrier wire.

References (fit ed in the file of this patent UNITED STATES PATENTS 7 2,899,528 Reichelt ;r Au 511f 2,930,879 Scatchard '..V Y Mar. 29, 1960 2,967,012 Connor Jan. 3, 1961 as a wire which is 

1. APPARATUS FOR EVAPORATING A MATERIAL WITHIN AN ION PUMP COMPRISING 